Conventionally, attractive type and repulsive type magnetic suspension apparatuses utilizing an electromagnet, a permanent magnet, and a ferromagnetic material have been used to levitate a movable part relative to a stationary part in a non-contacting manner.
Japanese Patent Application Laid-Open (kokai) No. 63-262056 discloses a suspension apparatus, applied to a motor, which utilizes repulsive force produced between a high temperature superconductor and a permanent magnet, i.e., force produced due to the Meissner effect.
Another mechanism which also utilizes a high temperature superconductor and a permanent magnet in combination has been proposed (the Linear Drive Study Group of the Institute of Electrical Engineers of Japan, Material No. 91-111, pp. 127-136). The mechanism utilizes force produced due to the so-called magnetic flux pinning effect to levitate and support a movable part. The pinning effect occurs when part of the magnetic flux produced by the permanent magnet is captured within the high temperature superconductor, and a force is produced to maintain the relative positional relationship between the permanent magnet and the high temperature superconductor. In this mechanism, the movable part is stably suspended with respect to the stationary part with a predetermined gap therebetween. Also, the position of the movable part in a direction perpendicular to the direction of the gap can be stably maintained such that the magnetic field applied from the permanent magnet to the high temperature superconductor does not change.
Since the force produced by the pinning effect is far larger than the force produced by the Meissner effect, the suspending stiffness can be increased.
However, in conventional suspension apparatuses using an electromagnet, a permanent magnet, and a ferromagnetic material, current must be continuously supplied to the electromagnet while the movable part is being suspended. Also, a large amount of electric power or a large electromagnet is needed to obtain a strong suspending force.
Moreover, the electromagnet must be arranged in each of a plurality of directions to safely maintain the movable part at a predetermined position.
Furthermore, when the gap between the stationary part and the movable part is controlled, the current supplied to the electromagnet must be always controlled based on the size of the gap which is fed back to the control section. In this case, the movable part slightly vibrates depending on the processing speed of the control circuit and the speed of sampling the size of the gap.
In the suspension apparatus utilizing the Meissner effect of a superconductor as disclosed in Japanese Patent Application Laid-Open No. 63-262056, a suspending force can be always obtained without using an electromagnet. However, since only repulsive force is produced between the superconductor and the permanent magnet, the apparatus is very instable by itself. Therefore, a mechanism must be added to maintain the predetermined gap and the predetermined position. Since the repulsive force due to the Meissner effect is very small compared to the magnetic attractive and repulsive forces of a magnet, the suspending force is small compared to the size of the apparatus.
The conventional suspension apparatus utilizing the pinning effect has the problem that the costs of the suspension apparatus increase because the permanent magnet is needed to obtain the suspending force, as in the suspension apparatus utilizing the Meissner effect. When the high temperature superconductor is disposed on the movable part, it becomes difficult to cool the high temperature superconductor and to maintain a cooled state. Hence, the high temperature superconductor is sometimes disposed on the stationary part while the permanent magnet is disposed on the movable part. In such a case, since the mechanical strength of the permanent magnet is lower than that of other mechanical members, the overall strength of the movable part decreases.
Moreover, when the high temperature superconductor is combined with only the permanent magnet, the kinds of objects which can be suspended are limited. In addition, when the movable part must be moved over a wide range in the direction perpendicular to the direction of suspension, high temperature superconductors or permanent magnets, which are both expensive, must be arranged over the wide range.
An object of the present invention is to solve the above-described problems and to provide a magnetic suspension apparatus which can stably produce a strong suspending and supporting force, which is cheap and has an increased mechanical strength, and which can permit a higher degree of freedom in designing the apparatus.
In the apparatus according to the present invention, a superconductor is cooled in a magnetic field of a single direction, and pinning flux penetrates the superconductor from one surface to the opposite surface thereof. Since a ferromagnetic material is disposed on one surface of the superconductor, the pinning flux penetrating the ferromagnetic material via a gap reaches the opposite surface while making a long detour through the space around the superconductor, thereby making a opened magnetic circuit. As a result, the magnetic resistance of the entire magnetic circuit increases, and the number of lines of magnetic flux of the ferromagnetic material decreases due to the increase of the magnetic resistance of the ferromagnetic material, so that the magnetic attractive force and the restoring force decrease. Therefore, another object of the present invention is to provide a magnetic suspension apparatus which can be improved to overcome the above-described problems.